Previous efforts at Cumbre Inc. have resulted in the discovery, characterization and optimization of a novel class of inhibitors of bacterial RNA polymerase The overall objective of this project is to establish the SAR of the Cumbre series as inhibitors of the RNA polymerase derived from M. tuberculosis, the causative agent of TB. These studies will involve the preparation and reconstitution of recombinant core and holoenzyme forms of M. tuberculosis RNA polymerase and the adaptation of current plate and gel format assays for the characterization of the mechanism of action of inhibitors of the M. tuberculosis enzyme. In addition, the Cumbre Inc. inhibitor series will be assessed for antibacterial activity against a panel of Mycobacterium species with the goal of establishing a strategy wherein future synthetic chemistry efforts may be directed toward the optimization of the series for activity against M. tuberculosis. Finally, additional studies will be focused toward establishing whether there may be any therapeutically relevant benefits of combining the Cumbre inhibitor series with rifampicin, a known inhibitor of bacterial RNA polymerase, which is clinically approved and currently used for the treatment of TB. Preliminary data obtained in Escherichia coli suggests that some mutations conferring resistance to rifampicin cannot be combined with mutations conferring resistance to the Cumbre series, and vice versa. Hence, the frequency of resistance to either agent may be reduced when the two classes of inhibitors are administered together in a single regimen. The results of the combined Phase I studies should provide a platform of data by which an informed decision can be made as to whether the Cumbre series has potential for future development as a novel antitubercular agent. Phase II studies would thereafter be addressed toward systematic optimization of the series as an antitubercular agent. [unreadable] [unreadable]